Exposure to atypical lighting conditions, like chronic darkness, during a critical period in development causes long-lasting deficits in the anatomy and function of the image forming visual system. Surprisingly, little is known about how abnormal lighting schedules affect the anatomy and function of the non-image forming visual system, a collection of subcortical retinorecipient nuclei. These nuclei mediate a variety of immediate and long-term light-responsive behaviors including sleep, circadian rhythms, visual attention, and pupillary constriction. We hypothesize that exposure to abnormal lighting schedules during early development will adversely affect the anatomy and function of sleep-wakefulness centers in the non-image forming visual system and may impair the ability of light-detecting neural networks to coordinate behavioral and physiological responses to light. To test this hypothesis, we will rear litters of albino rats in either constant light or constant dark from birth until adulthood. We will then use anterograde tracing to examine the connectivity of retinofugal fibers to subcortical targets (SA 1), use immediate early gene expression to analyze the molecular response of these neurons to acute light-dark shifts (SA 2), and use activity chambers and sleep recording electrodes to document sleep and circadian rhythms in response to light (SA3). Results from these studies will provide a first comprehensive analysis of the effects of light- and dark-rearing on sleep-wakefulness anatomy and function. Ultimately, a greater understanding of how early exposure to lighting schedules affects the developing sleep and circadian systems should provide insight into etiology of several sleep and circadian disorders.